CS198149B2 - Method of cleaning the combution products and gases - Google Patents

Description

The present invention relates to a process for the purification of flue gases and gases resulting from the combustion of fuels, and to a process for the production of sulfuric acid from sulfur-containing compounds isolated from said flue gases and gases.

Problems arise in cleaning flue gases and gases to remove sulfur compounds. known. In particular, difficulties arise in plants in which fuel oil or a mixture of fuel gas and fuel oil with a high sulfur compound content is combusted as fuel.

Among the chemical processes for the purification of the above-mentioned flue gases and gases, it is known in particular that the sulfur dioxide formed as a product of the combustion of sulfur compounds is subjected to an oxidizing action of a ferric sulfate solution.

In this process, sulfur dioxide is converted to sulfuric acid and ferric sulfate is reduced to. ferrous sulfate. In the next step of the process, ferrous sulphate is re-oxidized to ferric sulphate, which is achieved by bubbling the ferrous sulphate solution through the air, and neutralized with iron salts, especially oxides. Excess iron salts are isolated from the solution by evaporation and crystallization in the form of ferric sulfate. After drying, this sulfate is calcined to obtain iron oxides, which are then recycled to the appropriate stage of the process; sulfur dioxide can be used to produce sulfuric acid or to produce pure sulfur.

However, this method has some drawbacks.

One of these drawbacks is that the rate of oxidation of sulfur dioxide is low under the reaction conditions; this is especially true for low pH values. Accordingly, the scrubbing columns in which the gas / solution is in contact must have large dimensions.

In addition, the process steps in which the ferric sulphate is extracted from the solution, calcined into iron oxide and sulfur dioxide and converted into sulfuric acid are very complicated from the technical point of view and consequently costly.

In addition, the sulfuric acid resulting from the oxidation of sulfur dioxide with ferric sulfate contains a considerable amount of dithionic acid to which it is present. Separation is needed for a separate step.

The purpose of the invention is to eliminate these drawbacks by designing a process in which the above-mentioned flue gases and gases containing sulfur compounds can be cleaned up to a maximum sulfur yield using a simple and economical device.

The sulfur derivatives obtained, isolated in this way, should be convertible to sulfuric acid with minimum energy consumption.

It has now been found that when gas or flue gas and oxygen are contacted with a solution containing a metal salt such as cobalt, manganese or nickel, or a mixture of salts of at least two of these metals, at least one highly oxidized compound is formed, which, or which are capable of oxidising sulfur dioxide very rapidly and effectively.

The existence of these highly oxidized substances can be demonstrated by reaction with potassium iodide or by reaction with ferrous orthophenanthroline.

These highly oxidized compounds are important intermediates in the course of the reaction and are essentially coordination complexes such as [M ³⁺ (SO 3) 3] ³ , where M is a cobalt, manganese or nickel atom. The presence of this complex has been shown for cobalt including formula verification, it is interesting that this reaction usually does not occur spontaneously when the metal M is present exclusively in the divalent form. The sulfuric acid obtained by this oxidation process can be concentrated using heat supplied by the purified flue gases and gases. The sulfuric acid thus obtained corresponds to that of a commercially available acid.

Principle of a method for cleaning flue gases and gases derived from the combustion of fuels such as diesel by removing sulfur dioxide formed by oxidation of sulfur compounds, washing the flue gases and gases with at least one manganese salt-containing washing solution capable of oxidizing sulfur dioxide to form sulfuric acid in the presence According to the invention, an aqueous washing solution containing an oxidizing manganese compound having an oxidizing capacity corresponding to 4 milliequivalents of oxygen per liter of solution, manganese sulphate at a concentration of 10 to 20 g / kg of oxygen, optionally added to the flue gases and gases to be cleaned, 1 and at least 100 g / l of sulfuric acid are brought into contact with gases and flue gas optionally mixed with air, whereupon part of the washing solution containing the resulting sulfuric acid is concentrated and filtered to separate and crystallize manganese sulphate.

In the process according to the invention, a portion of the aqueous washing solution corresponding to a quarter to half of the total volume of the washing solution used is preferably removed from the contact with the gases or flue gases within 30 to 60 minutes of the gas and flue gas contact. the part is allowed to stand separately for at least one hour, after which the four are contacted with the cleaned flue gases or gases.

Preferably, the soot and ash contained in the flue gas and gases are removed prior to washing and possibly admixing the air with the flue gas and gases by pre-washing the flue gas or gases with a portion of the aqueous scrubbing solution with a corresponding amount of oxidized sulfur dioxide. such that the concentration of sulfuric acid in the wash solution remains constant.

The portion of the aqueous washing solution used to remove the soot and fly ash in the flue gas and gases is preferably concentrated and filtered to separate the soot and fly ash, whereupon the liquid portion is further concentrated under pressure.

10.6 kPa to precipitate manganese sulfate, which is then separated from the concentrated sulfuric acid. The manganese compounds whose manganese valency is greater than 2 and which are contained in said part of the aqueous solution to be washed are preferably reduced with sulfur dioxide during the pre-wash.

An advantage of the process according to the invention is that it allows efficient cleaning of the combustion gases under all conditions, while producing important sulfur compounds, in particular sulfuric acid, of a quality corresponding to the sulfuric acid conventionally supplied. This acid contains only traces of manganese sulphate. It should be pointed out that the process of the invention utilizes the heat supplied by the combustion gases; the necessary heat can of course also be supplied from an external source. From the foregoing, it is apparent that the process of the present invention can efficiently purify the combustion gases of sulfur compounds while producing concentrated sulfuric acid which is useful in the production of a variety of important chemical products.

In some cases, the cleaning process automatically stops at the moment when the amount of sulfur dioxide supplied exceeds the critical value given by the operating conditions.

Consequently, the following parameters have to be taken into account when carrying out the process according to the invention:

it is necessary to know the cross-section of the column in which the flue gas and gas are washed with an aqueous washing solution;

it is necessary to determine the column packing height necessary to ensure contact between the flue gas and gases and the washing solution;

it is necessary to determine the supply amount of the washing aqueous solution and the oxygen concentration in the flue gases and gases.

Based on the findings, the method according to the invention is carried out as follows:

A. First, the fill type is selected so as to achieve a predetermined specific fill surface.

B. The amount of flue gas and gas and the amount of washing solution corresponding to a predetermined pressure drop are then determined for the different filling heights and for the unit of height of the filling.

C. The retention volume of the filler used per unit of height is also determined as a function of solution delivery.

D. Calculate the quantity of sulfur dioxide vs flue gas and gas supplied per column height unit as a function of the different concentrations of oxygen in the flue gas and gas for each value of containment determined in accordance with point C.

E. Calculate the quantity of gases and flue gas supplied corresponding to the quantity of sulfur dioxide introduced in accordance with D. and select values for which the pressure drop corresponds to the value determined in accordance with B.

F. From the values obtained in accordance with point E., the values for which the quantity of sulfur dioxide fed in per unit height of the column is selected are determined and also, according to point E. the oxygen concentration, the amount of washing aqueous solution fed and the filling height.

G. Determine the cross-sectional area of the column from the relationship between the maximum flue gas and flue gas feed rates of point F, the fill height of point F., the amount of flushing water feed rate of point F. per unit column height and the oxygen concentration of the gases point F,

According to a characteristic embodiment of the method according to the invention, the contact between the flue gas and gases on one sulphate and the scrubbing solution on the other hand is achieved by using Raschig rings used as fillers in the scrubbing column.

According to another embodiment of the process according to the invention, the contact between the flue gases and gases on the one hand and the scrubbing solution is effected by dispersing the flue gases and gases in the scrubbing solution.

Preferably, the predetermined pressure loss is 600 Pa.

The sulfur dioxide feed rate of point D. should be maintained in a preferred ratio with respect to the oxygen concentration on the one hand and the retention volume on the other hand.

The concentration of sulfuric acid produced is also dependent on the amount of heat that is supplied by the flue gases and gases.

In addition, the amount of sulfuric acid obtained can be dependent on the amount of heat supplied by external sources, utilizing the heat supplied by the flue gases and gases to increase the speed of the process.

The invention also relates to an apparatus for carrying out the method according to the invention. It is a device for cleaning flue gases and gases, which simultaneously produces sulfuric acid.

The device according to the invention will be described with reference to the accompanying drawings, in which Figure 1 shows one embodiment of the device according to the invention, Figure 2 shows a second embodiment of the device according to the invention and Figure 3 shows a third embodiment of the device according to the invention.

The drawings therefore show an apparatus for purifying flue gases and gases containing sulfur dioxide using manganese salts.

For better understanding, the solids supply lines are drawn as solid lines and the gas lines are shown as dashed lines and the water vapor supply lines are. The lines for the liquid are plotted with double lines.

FIG. 1 shows a first embodiment of the device according to the invention. In this embodiment, the boiler 1, in which fuel 2 is used, is drawn. The resulting hot combustion gases containing sulfur dioxide are led first to a heat exchanger 2, the function of which will be described below, along arrow F1, then to chamber 3 according to FIG. arrow F2, where it mixes with the air supplied, for example, through the fan 4; from the fan 4 the air is supplied via the duct according to arrow F3. The resulting mixture is then passed through line F1 to the wash column 5, to which the wash solution is simultaneously fed to its top and circulation of this solution is ensured by the pump 6 along arrow E5. The column 5 is packed, for example, with Raschig rings (not shown) that provide contact between the scrubbed gas and the scrubbing solution, and then the scrubbed gas is discharged into the environment along the Fe arrow. The wash solution contains manganese sulphate and sulfuric acid, which is formed by oxidation of sulfur dioxide, as discussed below.

The portion of the wash solution that responds; providing the amount of sulfuric acid resulting from the oxidation of sulfur dioxide is passed from the bottom of the column 5 to the first filter 7 along arrow F7; said filter has the task of removing soot and ash, which are then emptied along the arrow F ». The arrow F9 indicates the direction in which the solution is discharged to the first buffer tank 8 to ensure regular flow of the solution, and then passes along the arrow F10 to the first evaporator 9. In the evaporator 9, the washing solution is thickened for the first time. it then passes along the arrow Fn to the second buffer tank 10 and from this tank along the arrow F12 to the second vaporizer 11 where the second thickening takes place. The concentrated solution is then passed along the arrow F13 to the third buffer tank 12 and then along the arrow F14 to the second filter 13 which separates a portion of the manganese sulphate, which is then passed along the arrow Fis to the tank 14, while the sulfuric acid is fed to tank 15 along arrow Fie. In addition, the double lines F17 indicate the circulation of a heating liquid which supplies the necessary heat, which is obtained in the gas and flue gas exchanger 2 and is fed to the first and second evaporators 9 and 11, where the sulfuric acid obtained is concentrated. The water vapor generated as a result of this concentration is passed along arrows Fie and F19 to the condenser 16 and then in liquid form along arrow F29 to the second filter 13 where it contacts the precipitated manganese sulfate, which in this way passes back to This solution is then fed back along arrow F21 to the bottom of the wash column 5. It will be appreciated that the condenser 16 and the first and second vaporizers 9 and 11 are kept under reduced pressure by the evacuation pump 17.

In addition, along arrow F22, a portion of the combustion gases from the exchanger 2 is brought into contact with the solution on the first filter 7 and then fed along arrow F23 to the bottom of the column 5 together with the mixture from the container. 7 directly into tray 3.

In addition, air from the evacuation pump 17 along the arrow F 24 can be led to the bottom of the column 5. The process according to the invention can here proceed as follows:

At the bottom of the column 5 a manganese sulphate solution is introduced, which preferably contains a small amount of manganese dioxide, which aids the reaction average. This solution is contacted in column 5 with a gas mixed with air which is fed along the arrow F4 from the container 3. The sulfur dioxide contained in the gases or flue gas dissolves in the solution and at the same time forms a complex of formula [Mn ^3+] (SO3) 3] ^3- complex or the like, and the presence of the complex and oxygen in air is formed at least one 0xidační agent which quickly oxidizes sulfur dioxide which is present in solution in free form and is converted to sulfuric acid. This enriches the wash solution with sulfuric acid. When the amount of sulfuric acid reaches a predetermined value, an amount of solution corresponding to the amount of sulfur dioxide absorbed is removed from the bottom of the column 5. This ensures that the sulfuric acid content of the wash solution remains stable.

The solution obtained from the bottom of the column 5 is filtered on the filter 7 and then passed along the arrow F10 to the first and second evaporators 9 and 11 to obtain concentrated sulfuric acid in the container 15. The manganese sulphate accumulates in the reservoir 14 after filtration through the filter 13, whereupon the water resulting from the condensation of the solution after condensation in the condenser 16 is fed along the arrow F20. The solution is then returned to the column 5 along the arrow F21. It should be emphasized that the concentration of sulfuric acid in the wash solution as well as the concentration in the solution coming from the first and second evaporators 9 and 11 is such that the heat of the combustion gases is sufficient to obtain sulfuric acid in the reservoir 15, the quality of which is similar to that of commercially available acids, without the need for additional heat.

In addition, it has been reported that at least a portion of the gas which has been contacted along the arrow F22 with the filter 7 and the extraction solution is fed along the arrow F23 to the bottom of the column 5. In this way, some manganese compounds can be reduced. 3 or

7. These compounds would contaminate the resulting acid.

The first embodiment of the process according to the invention can advantageously be carried out, for example, as follows:

Boiler 1 burns heavy fuel # 2, which contains 3.5% sulfur.

The gases and flue gases exiting the boiler 1 are fed to the exchanger 2 at a temperature of 160 ° C containing 30% excess air and having the following composition:

CO2 477 m ³ / h H2O 369 m ³ / h On 3 347 m ³ / h O2 214 m ³ / h SO2 7.5 m ³ / h the total gas supply is 4 414 m ³ / h

The gases leaving the exchanger 2 have an average temperature of 80 ° C.

In tank 3, the gases and combustion products are mixed with air at a rate of 6000 m ³ / h.

Upon exit from the following composition: stack 3 has gas CO2 4.77 m ³ 'h H2O 369 m ⁵ / h N2 8 087 m ³ / h 02 / 1474 m ³ / h S02 7.5 m ³ / h total supply of gases is 10 415 m ³ / h

The purified gas coming along the Fe arrow from the column 5 has a composition which is approximately the same as the above, provided that the maximum values of sulfur dioxide are 1 ppm, that is 0.01 m ³ per hour.

The proportion of gas passing along the arrow Fz? into the filter 7 represents approximately 10% of the total amount of gases entering the container 3.

In the continuous operation of the process according to the invention, the washing solution is fed along the arrow Fs having the following composition and in the following amounts:

manganese or equivalent amount

H 2 SO 2 total amount of solution

MnSCU 20 g / 1150 + 10 g / 1200 m ³ / h

The solution from the column 5 drawn by the arrow F7 has a similar composition to that described above; however, it is only discharged at 200 l / h.

Sulfuric acid is obtained in cartridge 15 at a rate of 20.8 Ph at a density of 1.73, and at a concentration of 80% by weight; this acid contains approximately 6 g of manganese sulphate per liter.

The solution that accumulates in the reservoir 14 is fed along the arrow F21 at a rate of 200 liters per hour, that is, per hour. feeds 3.875 kg of manganese sulphate back to column 5.

The various parts of the device according to the invention are to be made of a material which resists the substances guided by the device; a preferred material is polyvinyl chloride. The following are the dimensions and other details of each part of the device:

Box 5:

height 3 m, diameter 2.9 m; the column is filled to a height of 1 m with Raschig rings.

Pump 8:

power input 200 m ³ / h at discharge head 4 m. Filter 7:

filter for continuously performing the process with automatic washing of the filtered material.

Evaporator 9:

concentrated sulfuric acid at a concentration of 60% by weight accumulates at 4 kPa.

Evaporator 11:

concentrated 80% by weight sulfuric acid accumulates at 4 kPa.

Filter 13:

drum type or composition of horizontal sections.

Evacuation pump 17:. power input 400 m ³ / h, 4 kPa.

Exchanger 2:

two-stage type at temperatures of 120 and ° C; oil is used as the liquid.

Fan 4:

power input 6000 m ³ / h at a pressure of 500 Pa.

According to the second embodiment shown in FIG. 2, as in the first embodiment, heavy fuel No. 2 is combusted in boiler 1. Hot combustion gases containing sulfur dioxide are fed to a heat exchanger 2, the role of which has already been explained, namely: along arrow F1 and then into stack 3 along arrow Fx. In the container 3, the combustion gases are mixed with the air which is supplied, for example, from the fan 4. The air is supplied by the arrow F4 and the mixture formed in the container. 3 is then fed to the column 5 along arrow F4, and a wash solution is fed to its top and circulated by the pump 6 along arrow F5. The column 5 is packed with, for example, Raschig rings (not shown) which ensure optimal contact between the scrubbed gas and the scrubbing solution, whereupon the scrubbed gas is discharged into the ambient atmosphere along the Fe arrow. In particular, the scrubbing solution comprises manganese sulphate, sulfuric acid, which is the result of oxidation of sulfur dioxide in the combustion gases, as discussed below.

In addition, a portion of the wash solution corresponding to the amount of sulfuric acid formed is withdrawn continuously from the bottom of the column 5 to the first filter 7 along arrow F7, which filter is intended to remove soot and fly ash which is then removed along arrow Fe. The arrow Fs indicates the direction in which the solution is transferred to the first buffer tank 8, which is to maintain a uniform flow, and then passes along the arrow Fie to the first vaporizer 9. In this vaporizer, the solution is first concentrated and then along the arrow F11 to the second buffer tank 10 and therefrom along the arrow F12 to the second vaporizer 11 where the second thickening takes place. The concentrated solution is then passed along the arrow F13 to the buffer tank 12 and therefrom along the arrow F14 to a second filter 13, the purpose of which is to separate a portion of the manganese sulphate, which is then fed to the reservoir 14 along the flange ^. The concentrated sulfuric acid is fed along the arrow Fie to the reservoir 15.

In addition, the double lines F17 indicate the circulation of a heating liquid which supplies the necessary heat, which is obtained in the gas and flue gas exchanger 2 and leads to the first vaporizer 9 and the second vaporizer 11, where the sulfuric acid obtained is concentrated. The water vapor generated as a result of this concentration is passed along arrows Fie and F19 to the condenser 16 and then in liquid form along arrow F29 to the second filter 13 where it contacts the precipitated manganese sulfate, which in this way passes back to This solution is then fed back along the arrow F21 to the bottom of the wash column 5. It will be appreciated that the condensation device 16 and the first and second vaporizers 9 and 11 are kept under reduced pressure by the evacuation pump 17.

Furthermore, along arrows F22, a portion of the combustion gases from the exchanger 2 is contacted with the solution on the filter 7 and is then fed along arrow F23 to the bottom of the column 5 together with the mixture from the reservoir 3. filter 7 directly into the container 3.

In addition, it is possible to direct air from the evacuation pump 17 along arrow F24 to the bottom of the column 5.

In addition, in a second embodiment of the device according to the invention, a chamber 18 is introduced into the device, to which, for example, 1/4 of the washing solution from column 5 is fed. This fraction remains in the chamber 18 for a certain period of time. The solution is fed to the vessel by a pump along arrow F25, while the second pump provides for transfer of the solution after a certain maturation period back to the column 5 along arrow F28.

The method according to the second embodiment thus proceeds as follows:

A washing solution is fed to the bottom of the column. This solution is obtained as follows:

The mixture of the following composition is stirred for one hour:

hydrated manganese dioxide (MnOz.HžO) 10 g hydrated manganese sulphate (MnSO4.HaOj) 100 g sulfuric acid (H2SO4) 500 g water per liter

The mixture was filtered to separate the manganese dioxide. Following this procedure, the amount of oxidizing agent in the filtrate when measured at an optical density of 51 milliequivalents of oxygen per liter. Mixtures of the following compositions may also be used:

MnOž. H 2 O 0.5 g

MnSO ₄ . H2O 100 g

H2SO4 500 g

H2O up to 1 liter

The mixture was stirred for 30 minutes and then filtered.

The oxidizing agent content is 9.2 milliequivalents of oxygen per liter. Mixtures of the following composition may be used with the same result:

Μηθ2. H2O 0.6 g.

MnSCU. H2O 80 g

H2SO4 200 g

H2O up to 1 liter

The mixture was stirred for one hour and then filtered.

The oxidizing agent content is 4.7 milli-oxygen valents per liter. .....

Thus, it is clear that in some cases it is not necessary to separate manganese dioxide; in these cases, filtration is exhaled.

This means that the ratio of substances used can be in the following range:

Mn02. HzO MnSOd. H2O H2SQ4

H2O do

0.5 to 10 g 20 to 500 g 100 to 1000 g 1 liter

When using any of the above mixtures, the solution fed to the bottom of the column 5 is a filtrate which is diluted with water or a sulfuric acid solution such that the wash solution contains the following amounts of said compounds:

MnSOé. H2O 10 to 20 g / l

H2SO4 at least

100 g / l and optionally a small amount of manganese dioxide in the absence of filtration.

Said solution is contacted in column 5 with a gas mixture composed of combustion gases and air, the mixture is fed along arrow F4 from reservoir 3. Sulfur dioxide dissolves in this solution, forming a complex [Mn ³⁺ [SOojo] ³ or to form a similar complex in the presence of oxygen from the air, thereby forming at least one oxidizing agent which oxidizes the sulfur dioxide, which is present in free form in solution, relatively rapidly to sulfuric acid.

This enriches the wash solution with sulfuric acid. When the amount of sulfuric acid reaches a predetermined value, an amount of solution corresponding to the amount of sulfur dioxide absorbed is removed from the bottom of the column 5. As a result, the sulfuric acid content of the wash solution remains stable.

The solution obtained from the bottom of column 5 is filtered on the first filter 7 and then passed along arrow F10 to the first and second evaporators 9 and 11 to obtain concentrated sulfuric acid in the container 15. The manganese sulphate accumulates in the filter container 14 through the second filter 13, while water, which is formed during the thickening of the solution after condensation in the condenser 16, is fed along the arrow F20. The solution is then fed back to the column 5 along the arrow F21. It should be emphasized that the concentration of sulfuric acid in the wash solution as well as the concentration in the solution coming from the first and second evaporators 9 and 11 is such that the heat of the combustion gases is sufficient to obtain sulfuric acid in the storage tank 15, the quality of which is similar to that of commercially available sulfuric acid, without the need for additional heat.

In addition, it has been noted that at least a portion of the gas that has been introduced along arrow F22 in contact with the first filter 7 and with the extraction solution is fed along arrow F23 to the bottom of column 5. In this way, it is possible to reduce some manganese compounds in Manganese is equal to · 3

ΙΛ 1 ΤΡΙΟ Blllliémém These have polluted the resulting acid.

In addition, in some cases, the rate of oxidation of the sulfur dioxide with the scrubbing solution is so high that, initially, combustion gases per unit of scrubbing solution need to be introduced very rapidly, but in the course of this process this rate decreases substantially, usually after 30 minutes. up to 60 minutes. As already mentioned, it is sufficient to remove a portion of the solution and allow it to stand for about an hour, after which it can be returned to the process to achieve the original rate of oxidation.

This phenomenon may be explained by the maturing of the wash solution during standing, so that a sufficient amount of oxidizing agent is produced again.

This maturation does not seem to mean oxidation, because by bubbling air through the solution it is not possible to accelerate this process and the oxidation capacity of the solution also does not substantially change. It is possible that the cause of this phenomenon is the conversion of the aforementioned complex into another complex which is less suitable for oxides or sulphite ions; after a certain period of maturation, the original complex is formed again. During this conversion, the visible spectrum of the solution does not substantially change, whereas the optical density increases substantially, so that it has been found that the oxidation efficiency of the catalyst solution relative to sulfur dioxide increases with the optical density of the solution at 480-500 nm; in this case, the solution also has maximum absorption in visible light.

The following results were obtained when following these phenomena:

The wash solution produced as described above contains after 10 hours 140 g of sulfuric acid and 20 milliequivalents of oxygen per liter. The optical density of this solution is 0.200 at 500 nm.

After 3 hours standing, the optical density is 0.375 and after 96 hours 0.958. The oxidant content is still 20 milliequivalents per liter. Nevertheless, as the optical density of the catalyst solution increases on standing, its ability to purify the combustion gases is improved, thereby stabilizing the process of the invention, so that the dimensions of the scrubbing columns can be reduced and the amount of feed solution reduced relative to the amount of sulfur dioxide supplied.

To ensure this effect, a quarter or half of the volume of the wash solution is withdrawn from the bottom of the column 5 and this quantity is then passed along the arrow F25 to chamber 18 by the pump 19. The portion of the solution remains in chamber 18 for at least 1 hour, e.g. During this time, the solution matures, which is then fed back into the column 5 by the action of the pump 2C along the arrow F23.

After 30 to 60 minutes, remove part of the solution again and continue to _ββ ! Ϊ6ΜΠ1 as follows.

To illustrate this process, here is a specific example:

In the boiler 1 is burned heavy fuel no. 2 containing 3.5% of ^f ry. The gases and combustion products from this boiler are led to exchanger 2 and have a temperature of 160 ^° C; these gases contain a 30% excess of air and have the following reduction at the feed rate per unit of time.

CO2 477 m ³ / h H20 369 m ³ / b N2 3 347 m ³ / h O2 214 m ³ / h SO2 7.5 m ³ / h the total amount of 4 414 m ³ / h

The gases leaving the exchanger 2 have an average temperature of 80 ° C.

In tank 3, the gases and combustion products are mixed with air at a rate of 6000 m ³ / h.

When leaving the stack following composition: 3 has gas CO2 477 m ³ di H2O 369 m ³ / h N2 8 087 m ³ / h 02 / 1 474 m ³ / h SO ₂ 7.5 m ³ / h the total gas supply is 10 415 m ³ / h

Purified gas coming along column F6 from column 5 has a composition that is approximately identical to the above composition, provided that the maximum values of sulfur dioxide are 1 ppm, that is 0.01 m ³ per hour.

The proportion of gas passing along the arrow F22 from the exchanger 2 represents approximately 10% of the total amount of gases that are led from the exchanger 2 along the arrow F2 to the reservoir 3.

In the continuous operation of the process according to the invention, the following: feeds the wash solution along arrow F5 with the following composition and amount:

manganese or equivalent

MnSO 3 20 g / l

H2SO.1 150 + 10 g / l total solution volume 200 m ³ / h

The solution from column 5, discharged by arrow F7, is of comparable composition to the above solution; however, it is only discharged at 200 l / h.

Sulfuric acid is obtained in the reservoir 15 at a rate of 20.8 Vh at a density of 1.73 and a concentration of 80% by weight; this acid contains approximately 6 g of manganese sulphate per liter.

The solution accumulated in the reservoir 14 is fed along the arrow Fzt at a rate of 200 liters per hour; that is, 3.875 kg of manganese sulfate are fed back to column 5 per hour.

In this embodiment, 5,000 l of a solution of the above composition, prepared as described above, is fed to column 5.

In a continuous process, 2000 l of wash solution is removed from the bottom of column 5 every 30 minutes, this amount is allowed to stand for 1 hour in chamber 18 and then returned to column 5.

The various parts of the device according to the invention are to be made of a material which resists the compounds guided by the device, the preferred material being polyvinyl chloride. The following are the dimensions and other details of each part of the device:

Box 5:

height 3m, diameter 2.9 m, the column is filled to a height of 1 m with Raschig rings.

Pump 8:

power input 200 m ³ / h at discharge head 4 m. Filter 7:

filter for continuously performing the process with automatic washing of the filtered material.

Evaporator 9:

Concentrated acid at a concentration of% by weight accumulates at a pressure of kPa.

Evaporator 11:

concentrated 80% by weight sulfuric acid accumulates at 4 kPa.

Filter 13:

drum type or type consisting of horizontal sections.

Evacuation pump 17: power input 400 m ³ / h, 4 kPa.

Exchanger 2:

two-stage type, operating at temperatures of 120 and 80 ° C; oil is used as the liquid.

Fan 4:

power input 6000 m ³ / h at a pressure of 500 Pa.

Chamber 18: capacity 3000 l.

According to a third embodiment of the method of the invention as shown in FIG. 3, the boiler 50 consumes heavy fuel # 2. The hot combustion gases exiting the boiler and containing sulfur dioxide are fed first to the heat exchanger 51, the function of which will be described further along arrow F50 and into the column 52 where these gases are purged along arrow Fsi. This washing is preliminary and is therefore a preliminary column 52 in which the washing is carried out by circulating the washing liquid by means of a pump 53 along the arrow Fss. The scrubbing column 52 is packed with, for example, Raschig rings to ensure optimal contact between the gas and the scrubbing solution.

The gas is then fed along the arrow F53 to the reservoir 54. In this reservoir, air is admixed, for example, along the arrow F54 from the fan 55. The resulting mixture is then fed along the arrow F55 to a wash column 58 at the top of which wash solution is fed. whose circulation is ensured by the pump 57 along the arrow Fss. The column 56 is also packed with Raschig rings (not shown) which ensure optimal contact of the gas with the scrubbing liquid. The gas to be cleaned then enters the ambient air along arrow F57. The wash solution comprises manganese sulfate and sulfuric acid, which is formed by oxidation of sulfur dioxide from the combustion gases, as will be explained below.

In addition, a portion of the combustion gas scrubbing solution corresponding to the amount of sulfuric acid formed by oxidation of sulfur dioxide from the combustion gas is continuously discharged from the bottom of column 56 and fed to the pre-wash column 52 by the metering pump 58 along arrow F58. .

The solution leaving the prewash column 52 is passed to the filter 59 along arrow F59, the soot and fly ash are removed from the filter, which are then accumulated and drained along the Feo arrow. The arrow Fsi indicates that the solution is then transferred to a buffer tank 60, the purpose of which is to ensure a uniform supply along the arrow F62 to the vaporizer 61. In this vaporizer! there is a second concentration of the solution, the first concentration of the solution was carried out in the prewash column 52, then the concentrated solution is passed along the arrow Fsi to the buffer tank 62 and therefrom along the arrow F64 to the filter 63 which removes part of the manganese sulphate it is fed to the reservoir 64 along the arrow Fes, whereas the concentrated sulfuric acid is fed to the reservoir 65 along the arrow Fee.

The double lines F67 illustrate the circulation of the liquid that conducts heat from the exchanger 51 to the evaporator 61, in which the sulfuric acid is finally thickened. The water vapor produced as a result of this concentration is passed along arrow F67 _and to the condenser 66 and then passed along arrow F6 # back to the filter 63 where it comes into contact with manganese sulphate, which in this way is brought back into solution and then fed to the shelf 84 along the arrow Fss. The resulting solution is then fed along the arrow Fse to the bottom of the wash column 56. The condenser 88 and the vaporizer 61 are kept under reduced pressure by means of an evacuation pump 67.

The arrow F10 indicates that air from the evacuation pump 67 is fed to the bottom of the wash column 53.

The method of using the apparatus of the third embodiment can thus be explained as follows:

A manganese sulphate solution, preferably with the addition of a small amount of manganese dioxide, is fed to the bottom of the column 58 to facilitate the reaction.

This solution is preferably prepared as described above.

The solution in column 56 is contacted along the arrow Fss with the gas from which the soot and fly ash in the prewash column 32 has been removed and which has already been mixed with air in the reservoir 54 from which it is then discharged along the arrows Fss. Sulfur dioxide from combustion gases in the wash solution dissolves and forms the complex [Mn ³⁺ (SO] 3] ³ - or a similar complex, from which is produced in the presence of oxygen from air at least one strong oxidizer that rapidly oxidizes sulfur dioxide which is in solution in free, ionized or compound form to sulfuric acid.

In this way, the acid concentration in the wash liquid is increased.

When this concentration reaches a predetermined value, a quantity of washing solution is taken from the bottom of the column 5S corresponding to the amount of sulfur dioxide absorbed. As a result, the concentration of sulfuric acid in the wash liquid remains constant.

The withdrawn solution is fed to the pre-wash column 52 along the arrow Fss and serves, on the one hand, to remove the soot and fly ash in the gas that is fed along the arrow Fsi, on the other hand the first concentration of the solution so that the sulfuric acid content 40% by weight.

The water vapor produced as a result of this concentration is passed to the wash column 56.

In addition, in the pretreatment column 52, sulfur dioxide reduces some of the manganese compounds in which the manganese has a higher than 2, for example 3 or 7, these compounds could in some cases interfere with the reaction or cause contamination of the resulting acid.

The solution removed from the pre-wash column 52 as described above is passed along arrow F59 to a filter 59 where it is stripped of soot and ash and then re-concentrated in the evaporator 61 so that sulfuric acid is formed in the reservoir 85. . The manganese sulphate, which accumulates in the reservoir 84 after filtering through filter 63, is fed along arrow Fe9 to the bottom of column 56. This solution was obtained along arrow ββ from column 52 for prewashing after condensation in condenser 66 as described above. In this way, sulfuric acid is produced only by the action of heat supplied by the combustion gases. In this way, sulfuric acid of a similar quality to that of commercially available sulfuric acid is thus obtained, without the need for additional heat.

Hereinafter, a specific example of a third embodiment of the method according to the invention will be given.

Boiler 58 consumes heavy fuel # 2, which contains 3.5% sulfur.

The gases and combustion products produced in the boiler 50 are fed to the exchanger 51 at a temperature of 160 ° C, in which it is mixed with

approximately 30% surplus then the following composition: air and have CO2 4.77 m ³ / h m ³ / h H2O 369 N2 3 347 m ³ / h 02 / 214. m ^{3 /} h SO2 ' 7.5 m ³ / h total supply 4 414 m ³ / h

The gases leaving the exchanger 51 have an average temperature of 100 ° C and are fed to the prewash column 52 from where they exit at a temperature of about 60 ° C.

In the container 54 the combustion gases are mixed with air in a total amount of 6000 m ³ / h.

Upon exit from the following composition: sobníku 54 have CO2 477 m ³ / h H: <0 560 m ³ / h N.2 8 087 m ³ / h O2 1 474 m ³ / h SO2 7.5 m ³ / h total supply 10 600 m ³ / h

The purified gases that are discharged from the column 56 along arrow F57 have a similar total feed and a content of approximately 1 ppm sulfur dioxide, i.e. 0.01 m ³ per hour.

In continuous operation, the wash solution fed along the arrow Fss has the following composition:

manganese or an equivalent amount of MnSOt of 20 g / l

H2SO4 150 + 10 g / l total supply 200 to 400 m ³ / h

The solution, which is fed back continuously to the prewash column 52 along the arrow F52 and provides contact between the combustion products and the wash solution, has the following composition:

manganese or an equivalent amount of MnSCU of 60 g / l

H2SO4 500 g / l total feed 100 m ³ / h

The solution, which is passed from the pre-wash column 52 to the vaporizer 61, has the same composition, but its total feed is only 65 l / h.

Sulfuric acid is recovered in cartridge 85 in an amount of 20.8 L and has a density of 1.73 and a concentration of about 80% by weight; this acid contains about 6 g of manganese sulphate per liter.

The manganese sulphate solution in reservoir 64, which accumulates at a total amount of 200 l / h, contains approximately 3.875 kg of manganese sulphate over the same period of time and passes along arrow F69 to the bottom of column 56.

The various parts of the device according to the invention are to be made of materials which resist the action of the compounds guided by the device; a preferred material is polyvinyl chloride. The different parts of the device have the following size:

Box 52:

height 3 m; diameter 2 m; the column is filled to a height of 0.75 m with Raschig rings.

Box 56:

height 3 m; diameter 2.9 m; the column is filled to a height of 1 m with Raschig rings.

Pump 57:

power input 200 to 400 m ³ / h at discharge head

m.

Pump 53:

power input 100 m ³ / h at a discharge height of 4 m.

Filter 59:

filter for continuous automatic washing.

Evaporator 61:

Evaporator for sulfuric acid at 80% by weight at 4 kPa.

Filter 63:

drum type or type consisting of horizontal sections.

Evacuation pump 67:

power input 100 m ³ / h at 4 kPa.

Exchanger 51:

single stage heat exchanger, operating at temperatures of 160 and 110 ° C; oil is used as the liquid.

Fan 55:

power input 6000 m ³ / h at a pressure of 500 Pa.

In the prewash column, in addition to the removal of soot and fly ash, the first concentration of sulfuric acid to 40 wt. In this way, it is possible to use only one evaporator 61 and, moreover, to use only a one-stage exchanger 51, whose heat exchange is much more advantageous than in the absence of a pre-wash column.

As already mentioned, the reaction can be solved or even stopped if the sulfur dioxide supply exceeds a critical value which depends on the operating conditions. In this case, the oxidizing agents are reduced so that all manganese compounds have a manganese valency of 2.

This finding supports the idea that, on the one hand, sulfur dioxide induces the formation of oxidizing agents and, on the other hand, it reduces these agents during the reaction. It is believed that if the sulfur dioxide concentration is too high, only the oxidation reagents are completely reduced and the reaction is stopped in the wash column.

According to the invention, the total amount of sulfur dioxide supplied and thus the total amount of combustion gases supplied is a function of a number of parameters. Sulfur dioxide should be fed in proportion to the oxygen concentration, especially in the gas mixture that is fed to column 5 of Figures 2 and 1 or to column 56 of Figure 3.

The total amount of sulfur dioxide supplied must also be reconciled with the 3 retention volume in the washing pan 5 or 56.

It is known that the containment volume is defined as that amount of liquid that is present at any time in a device that is included in a continuous process.

The volume of retention therefore depends mainly on the total liquid supply.

In the case of column 5 or · 53, the containment volume depends on the inlet, wash solution and also on the column load. Especially when the fill is formed by Raschig rings, the containment volume is dependent on the total surface of the Raschig rings.

For this reason, it can be assumed that the total sulfur dioxide supply will be higher the higher the containment volume and the oxygen concentration in the gas mixture.

Also, pressure losses increase depending on the containment volume and the total gas supply.

It is therefore important to determine the total pressure drop during the continuous operation of the process of the invention and to achieve an optimum ratio of the basic parameters of the process of the invention so that the purified gases leaving column 5 or 56 along the arrows Fe or F57 never contain more than 20 ppm sulfur dioxide; so that this value is preferably near 1 ppm.

In the examples described below, a total pressure drop equal to 60 mm water column is reported, which corresponds to the value normally accepted for a boiler, and this value is also used to determine optimal conditions in which the gas to be cleaned contains no more than 20%. ppm of sulfur dioxide.

In all cases, a boiler is used which burns heavy fuel No. 2 containing 3.5 percent sulfur.

Under these conditions, the following relationship applies:

D = 0.03 (O2) ² . containment volume -j- A in which

D is the sulfur dioxide intake in liters per hour per m ^{2 of the} cross-section of the washing column 5 or 53.

(O 2) means the percentage of oxygen in the gas mixture as a percentage of column 5 or 58; this concentration is in the range of 10 to 21% by volume of oxygen;

the volume of retention is given in liters of solution per m ^{2 of the} cross-section of the column;

A is a constant that corresponds to a sulfur dioxide feed that is directly oxidized without forming a coordination complex.

For columns filled with Raschig rings, the value of A in all cases is 550.

From the experimentally established relationships, it is possible to recommend a method of optimum ratio of parameters in carrying out the method according to the invention as follows:

first and foremost, the packing of the column is put in place according to the shape and specific surface area, for example using Raschig rings of the indicated dimensions;

(b) the gas supply and solution supply shall be determined for different packing heights and column cross sections so that the pressure drop is equal to 60 mm water column;

(c) the values of containment volume per specified cross-sectional unit are determined as a function of solution supply relative to the filling height;

(d) the oxygen concentration and, as a result, the concentration and supply of sulfur dioxide, which can be oxidized efficiently under those conditions, shall be calculated for each value determined, the containment volume; the above equation shall be used for the determination;

(e) in accordance with this equation, the maximum supply of sulfur dioxide is greater the retention volume and the oxygen concentration; it goes without saying that, at the same time, there is also an increase in pressure drop; a gas supply at a pressure drop of 600 Pa shall therefore be determined for each value of the containment volume at a given filling height; in this gas supply, the desired sulfur dioxide supply and optimum oxygen concentration can then be determined;

(f) from the values thus obtained, the maximum possible sulfur dioxide inlets are obtained for various values of the various parameters, such as filling height, oxygen concentration in the gas mixture, washing liquid supply, so that the pressure drop across the charge is equal to 600 Pa; the values measured under (e) shall be those for which:. the sulfur dioxide supply is the highest. Other parameters, such as filling height, oxygen concentration and solution supply, correspond to this supply.

(g) The values defined in point (f) shall be related to a unit of cross-section equal to 1 m ^z . This makes it easier to calculate the entire device for operation under optimal conditions. If, for example, a boiler with a maximum sulfur dioxide supply is included, as calculated from the maximum hourly fuel consumption of the boiler and the maximum sulfur content of the fuel, the parameters of the gas purification plant can be calculated as follows:

the filling height is defined according to f, the oxygen concentration in the gas is calculated according to f, the cross-section of the column - luh. maximum SO2 inlet from boiler maximum SO2 inlet according to f) solution inlet - inlet according to f).

. cross-section of column;

(h) the parameters defined in (f) are a function of the packing characteristics such as specific surface area, pressure reduction and the like; in the case of Raschig rings, the larger the specific surface area, the lower the volume and height of the column and the larger the cross-section of the column; the choice of filling is made according to local conditions, such as height and possible surface area, and also depends on economic conditions such as the cost of the materials used,

The following examples illustrate the invention.

Example 1

Raschig rings of 15 mm diameter and 15 mm height are used.

The specific surface area of these rings is 292 m ² / m ³ .

This means that under optimal conditions the following parameters can be achieved:

24 the sulfur dioxide supply is 1080 l / h / m ^{2 of} cross-section;

the total supply of gases fed to the column is 1300 m ³ / hhn ² ;

the oxygen concentration in these gases is 13% by volume; filling height is 1 m;

the total supply of washing solution is 40 m ³ / h / m 2.

This means that in a plant that consumes 300 kg of heavy fuel # 2 containing 3.5% sulfur dioxide per hour, the wash column has the following characteristics:

cross-section = 7 m ² ;

filling height - 1 m;

diameter = 3 m;

volume - 7 m ³ ;

feed rate = 280 m ³ / h.

Example 1 and d 2

Raschig rings of 25 mm diameter and 25 mm height are used. The specific surface area of these rings is 195 m ² / m ³ . Under optimal conditions, the following parameters can be achieved in the wash column:

the sulfur dioxide supply is 1115 l / h / m ^{2 of} cross-section;

the total supply of gases fed to the column is 1560 m ³ / h / m ^{2 of} cross-section;

the oxygen concentration in said gas mixture is 13.6% by volume;

filling height 1.4 m;

the total supply of washing solution is 50 m ³ / h / m ^{2 of} cross-section.

This means that with a No. 2 heavy fuel consumption of 3.5 kg of sulfur at 300 kg / h, the wash column has the following dimensions:

cross-section = 6.7 m ² ;

diameter = 2.9 m;

filling height = 1.4 m;

volume = 9,4 m ³ ;

feed rate = 335 m ³ / h.

Example 3

Raschig rings of 50 mm diameter and 50 mm height are used. The specific surface area of these rings is 98 m ² / m ³ . Under optimal conditions, the following parameters of the device according to the invention can be achieved:

the sulfur dioxide supply is 1290 l / h / m ^{2 of} cross-section;

the total supply of gases fed to the scrubbing column is 1835 m ³ / h / m ^{2 of} cross-section;

the oxygen concentration in the feed gases is 14 vol.

filling height is 2.5 m;

total supply of washing solution is 65 m ³ / h / m ^{2 of} cross-section.

This means that when using a boiler in which 300 kg of fuel No. 2 containing 3.5% of sulfur is consumed per hour, the following column dimensions can be achieved in the plant according to the invention:

<1

cross-section = 5.85 m ² diameter = 2.73 m filling height = 2.5 m volume = 14.6 m ³ solution inlet = 380 m ³ / h

Example 1 a d 4

No Raschig rings or other packings are used, but the scrubbing liquid is dispersed in countercurrent to the gas stream in the scrubbing column. Dispersing conditions corresponding to a theoretical specific surface area of 66 m ² / m ³ . Under these conditions, the following parameters can be achieved in carrying out the process of the invention:

the sulfur dioxide supply is 1 940 l / h / m ^{2 of} cross-section;

the total gas supply to the scrubbing column is 3,400 m ³ / h / m ^{2 of} cross-section;

the oxygen concentration in the feed gas is

15.2% by volume;

the column height is 4 m;

the supply of washing solution is 100 m ³ / h / m ^{2 of} cross-section.

Under these conditions, the following column parameters can be achieved with a boiler burning 300 kg of heavy fuel # 2 containing 3.5% sulfur per hour:

cross-section = 3,86 m ² diameter = 2,2 m column height = 4 m volume - 1 514 m ³ solution inlet = 386 m ^{3 /} h

In this way, in all cases, a maximum of 20 ppm sulfur dioxide can be obtained, with a pressure drop of 600 Pa.

It will be appreciated that in the examples and under the conditions set forth, the optimum parameters of the apparatus for the purification of the combustion gases may vary, in particular according to local conditions, without embodiments falling outside the scope of the invention. In particular, the column height, the cross-section of the wash column can be varied under the conditions mentioned.

The process according to the invention thus makes it possible, under all conditions, to ensure efficient purification of the combustion gases and, moreover, to produce various sulfur derivatives, in particular sulfuric acid, the quality of which corresponds to the quality of commercially available sulfuric acid so that it can be used directly for various chemical purposes. This acid contains traces of manganese sulphate.

It is also obvious that a number of devices according to the invention can be arranged in series or side by side.

In addition, cobalt, nickel or mixtures of these metals may also be used instead of manganese, or the process of the invention may be carried out initially with one of these elements and proceeded with the use of another element, with advantageous reaction and perfect combustion gas purification.

It should be emphasized that the process of the present invention utilizes heat which is supplied by the combustion gases, but the same process can be carried out, if necessary, by bringing heat from any external source. In this case, it is possible to use heat from the combustion gases to accelerate the gas output from the device according to the invention so that these gases are rapidly dispersed in the atmosphere.

Thus, it is clear that the process of the present invention can efficiently purify the combustion gases of sulfur-containing compounds while producing concentrated sulfuric acid, which is directly applicable to a variety of purposes.

In particular, the process according to the invention and the apparatus for carrying out the process can find their use in heating plants and industrial plants in which materials with an increased sulfur content are used as fuel.

It goes without saying that the invention is not limited to the described embodiments.

In particular, it is possible to make changes in the apparatus according to the invention, in particular as regards the supply of individual materials and other parameters. In particular, it is possible to replace individual parts of the device with other elements having the same function.

Claims (4)

A process for the purification of flue gases and gases derived from the combustion of fuels, such as diesel, by removing sulfur dioxide formed by oxidation of sulfur compounds, by washing the flue gases and gases with at least one manganese salt-containing washing solution capable of oxidizing sulfur dioxide to form sulfuric acid; in the presence of oxygen optionally added to the flue gas and gases to be scrubbed, characterized in that an aqueous washing solution containing oxidizing manganese, a compound having an oxidizing capacity corresponding to 4 milliequivalents of oxygen per liter of solution, manganese sulphate in a concentration 10 to 20 g / l and at least 100 g / l of sulfuric acid are brought into contact with gases and flue gas optionally mixed with air, whereupon part of the washing solution containing the resulting sulfuric acid is concentrated and filtered to separate and crystallize manganese sulphate. 2. A method according to claim 1, characterized in that within 30 to 60 minutes of the gas or flue gas contact with the scrubbing solution, a portion of the aqueous scrubbing solution corresponding to four to one half of the total volume of the scrubbing solution used is removed. gases or flue gases, and this part is allowed to stand separately for at least one hour, after which it is brought back into contact with the purified flue gases or gases. 3. The method of claim 1, wherein the soot and fly ash contained in the flue gas and gases are removed prior to washing and optionally admixing air with the flue gas and gases by pre-washing the flue gas or gases with a portion of the aqueous washing solution corresponding to oxidized sulfur dioxide. Replace this portion with an appropriate amount of fresh solution so that the concentration of sulfuric acid in the wash solution remains constant. 4. The process of claim 3 wherein the portion of the aqueous washing solution used to remove the soot and fly ash in the flue gas and gases is concentrated and filtered to separate the soot and fly ash, and the liquid portion is further concentrated at 10.6. KPa to precipitate manganese sulfate, which is then separated from concentrated sulfuric acid.